Recently, addition of multiple functionalities to and down-sizing of mobile-related devices have been rapidly required. With this expansion, needs for high-density packaging technologies of semiconductor elements have been increased each year, in particular, the development of stacked multichip packaging (hereinafter referred to as “stacked MCP”) in which semiconductor elements are laminated takes a central role.
In the development of the stacked MCP technology, two contrary goals, that is, down sizing of the package and multi-layer lamination are combined. In order to achieve the goals, technologies for making the thickness of silicon wafer used in semiconductor elements thinner have particularly been advanced, and wafers having a thickness of 100 μm or less have widely been used and studied. Also, since the multi-layer lamination complicates a package making step, it is demanded to simplify the package making step and to suggest making processes and materials that support the increase of the number of heat histories of wire-bonding by the multi-layer lamination.
Under the circumstance, as an adhesive material of the stacked MCP, paste materials have been used. The paste materials, however, have some problems such that run-out of a resin is caused in a bonding process of semiconductor elements, or the degree of precision of the film thickness is low. These problems cause failures in a wire-bonding step or voids in a paste agent, and consequently, when a paste material is used, the above-mentioned requirement cannot be addressed.
In order to improve the above-mentioned problems, these days, it tends to use an adhesive in the state of a film instead of a paste material. The adhesives in the state of a film can adjust an amount of a resin run-out smaller than paste materials, and can make the variation of film thickness smaller by improving a degree of precision of a film thickness, and, therefore, the application thereof to the stacked MCP is particularly widely studied.
The adhesive in the state of a film has usually a structure in which an adhesive layer is formed on a release substrate. One of the typical methods for using the adhesive in the state of a film is a method for sticking to a back surface of a wafer. The method for sticking to a back surface of a wafer is a method in which an adhesive in the state of a film is directly stuck to a back surface of a silicone wafer used in the production of semiconductor element. According to this method, after the adhesive in the state of a film is stuck to the semiconductor wafer, a release substrate is removed, and then a dicing tape is stuck to the adhesive layer. After that, it is mounted on a wafer ring, and the wafer is cut in a desired semiconductor element size together with the adhesive layer. The diced semiconductor elements have the adhesive layer having the same size as the element. The semiconductor elements with the adhesive layer are picked-up and stuck to a substrate for mounting the elements in a thermo compression bonding method, or the like.
Dicing tapes used in the method for sticking to a back surface have usually a structure in which a tacky layer is formed on a substrate film, and roughly divided into two kinds of the pressure-sensitive dicing tape and the UV type dicing tape. The dicing tapes are required to have, as one function, sufficient tack strength so that semiconductor elements are not scattered by a load generated when the wafer is cut in a dicing step. In addition, it is demanded that when the diced semiconductor elements are picked-up, the tacking agent is not left on each element, and therefore, the semiconductor element with the adhesive layer can be easily picked-up in a die bonder apparatus.
In order to shorten a step for making a package, the requirement of further process improvement has been increased. According to conventional methods for sticking to a back surface of a wafer, two steps are necessary, that is, a step in which adhesive in the state of a film is stuck to a wafer and a subsequent step in which a dicing tape is stuck. In order to simplify this process, adhesive sheet (die bond dicing sheet) having two function of an adhesive in the state of a film and a dicing tape. As this type of the adhesive sheet, a laminate type having a structure in which an adhesive in the state of a film and a dicing tape are laminated (see, for example, Patent Documents 1 to 3), and a mono-layered type in which one resin layer has both functions of a tacky layer and a adhesive layer (see, for example, Patent Document 4) are proposed.
Also, a method in which such an adhesive sheet is previously processed into a shape of a wafer constituting a semiconductor element (generally called as precut processing) is known (for example, Patent Documents 5 and 6). This precut processing is a method in which the resin layer is punched into a shape matching that of a wafer used, and a part of the resin layer other than the part to which the wafer is stuck is peeled off.
When such a precut processing is performed, the laminate type adhesive sheet is generally produced by a method in which an adhesive layer in an adhesive in the state of a film is subjected to precut processing matching with a shape of a wafer, and after it is laminated on a dicing tape, the dicing tape is subjected to precut processing for matching with a shape of a wafer ring, or a dicing tape which has previously been subjected to precut processing into a shape of a wafer ring is laminated an adhesive in the state of a film which is subjected to precut processing.
Also, a mono-layered type adhesive sheet is generally produced by a method in which a resin layer having two functions of an adhesive layer and a tacky layer (hereinafter referred to as “tacky-adhesive layer”) is formed on a release substrate, the tacky-adhesive layer is subjected to precut processing, unnecessary parts of the resin layer are removed, and then it is laminated on a substrate film.    [Patent Document 1] Japanese Patent No. 3348923    [Patent Document 2] Japanese Patent Application Laid-Open Publication No. 10-335271    [Patent Document 3] Japanese Patent No. 2678655    [Patent Document 4] Japanese Patent Application Laid-Open Publication No. 7-15087    [Patent Document 5] Japanese Utility Model Application Laid-Open Publication No. 6-18383    [Patent Document 6] Japanese Utility Model No. 3021645